While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using a KrF, ArF or F2 laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.3 μm or less. Various alkali-soluble resins are used as the base resin in such resists.
For KrF laser resists, a polyhydroxystyrene resin having phenolic hydroxyl groups as the alkali-soluble functional group is, in fact, a standard base resin. For ArF laser resists, poly(meth)acrylate resins and resins comprising polymerized units of cycloaliphatic olefin such as norbornene, using carboxyl groups as the alkali-soluble group, are under investigation. Of these, the poly(meth)acrylate resins are regarded, due to ease of polymerization, as a promising candidate for practical use. These resist resins using carboxyl groups as the alkali-soluble functional group, having a higher acidity than phenolic hydroxyl groups, however, tend to encounter difficulty of dissolution control, often leading to pattern collapse caused by swelling or the like.
Functional groups having an acidity comparable to phenolic hydroxyl groups are desired. It was proposed to use an alcohol having plural fluorine atom substitution at α- and α′-positions (e.g., having a partial structure: —C(CF3)2OH) as the alkali-soluble functional group, as described in G. Wallraff et al., Active Fluororesists for 157 nm lithography in 2nd International Symposium on 157 nm Lithography. Styrene and norbornene derivatives having fluoroalcohol —C(CF3)2OH incorporated therein are proposed as monomers used in the manufacture of base resins. Similar examples of fluoroalcohol-substituted norbornene are found in JP-A 2003-192729 and JP-A 2002-72484. For the polymerization of norbornene monomers, however, radical polymerization of monomers of the same type is difficult, and instead, special polymerization techniques such as coordinate polymerization and ring-opening metathesis polymerization, using unique transition metal catalysts are necessary. Although alternating copolymerization of a norbornene monomer with a comonomer such as maleic anhydride or maleimide can be performed by radical polymerization, the presence of comonomer imposes a substantial limit on the freedom of resin design.
JP-A 2003-040840 describes fluoroalcohol-substituted acrylate monomers. Although the method of preparing these monomers is not definite, the starting material used is hexafluoroacetone (boiling point −27° C.) which is awkward to handle because it is gaseous at room temperature. The synthesis of polymerizable compound must follow long steps, leaving the problem that commercial preparation is difficult.
There is a strong demand to develop an easily prepared polymerizable compound having both a (meth)acrylate structure that facilitates polymerization or making a resist resin and a functional group that has an acidity comparable to phenolic hydroxyl.